A rolling line for wire incorporates rolling and water-type thermal treatment stages which reduce a billet to a wire, here intended to cover any very long workpiece of uniform cross-sectional size and shape, whose leading and trailing ends are of imperfect structure. Thus it is necessary to crop and recycle these ends. It is also necessary to longitudinally subdivide some very long wires for reeling or finish milling.
Since efficiency and the need to prevent blockages at the rolling stands require the use of high transport speed--5000 to 10,000 feet/minute--for the wire while keeping it under substantial tension, the shear must be able to work on a rapidly moving and taut workpiece. Flying shears which move rapidly along with the workpiece have been used, but have been found extremely wasteful of space in the mill.
Accordingly resort has been had to drum-type or rotating shears having blades which rotate at a peripheral speed equal to the wire transport speed. These blades are provided on drums or heads rotatable about parallel superposed axes in such a manner that with each rotation the blades pass closely, normally with the upper blade ahead in the travel direction of the lower blade. The heads are formed with identical helical grooves that form a row of passages at the nip between the two rollers. Immediately downstream of the shear there is provided a so-called discharge unit having three horizontally spaced holes, for receiving the front end part, the rear end part, and the good center part.
As described in East German patent documents Nos. WP B 23, D/221 156 and WP B 23 D/221 154 the wire passes upstream of the shear through a horizontally swingable guide tube that pushes it at the right moment into the end of the nip between the two cutter heads so that the wire is then entrained by the mating helical grooves and is pulled across to the blades where it is cut. The trailing part of the wire then continues across as the heads rotate. This system can accurately crop the ends from the wire, but requires two separate shears, one to crop the leading end and one to crop the trailing end. In addition the guide tube can only swing back to the starting position once the wire has completely passed through, that is between billets, so the system is slow.
It has been suggested in East German patent document 145,237 to use a shear of the above-described general type, but where the heads can be swung apart so that the guide tube can be returned to its starting position between cuts. Such an arrangement can be made fairly compact, but is itself a very complex machine. The universal joints necessary for the head drive shafts are complex, as is the support mechanism necessary for holding the cutter heads together for shearing the workpiece. Making the system work with the proper synchronization for an accurate cut requires complex control equipment.